Hollow towers are used in many different applications, as for instance wind energy converters, meteorological masts, telecommunication towers, lamp posts, watch towers or lighthouses.
In many cases, in these applications it is necessary to foresee a system which allows reaching the upper part of the tower, for operation or maintenance reasons.
The simplest system for this aim is a ladder attached to the tower, either internally or externally. However, in higher towers this solution can be inadequate, due to the effort necessary to climb to the top of the tower and the safety issues involved. On the other hand, outer ladders have a bad effect on the installation aesthetics, and internal ladders need additional lighting equipment.
In very large towers, an internal lift is a common solution, although the space required inside the tower and the cost of the installation makes it unaffordable for medium size towers.
There are also “medium size” installations where ladders are not convenient whether an internal lift is technically unfeasible and/or economically unaffordable. In these installations, a common solution is the use of lifting devices which are able to climb on wires arranged on the outer side of the tower and supported on it.
In the simplest version of this solution, the wires are permanently in their working position, hanging from a support at the tower top. The advantage is that not movable parts are used and the operators do not have to prepare the installation for using the lifting device. However, this option is not always possible due to the normal operation of the installation, for instance in wind turbines, where the wires can interfere with the rotor blades turning. On the other hand, a disadvantage of keeping the wires outside of the tower permanently is that they are exposed to corrosion and other environment aggressions, as well as vandalism acts. Additionally if the wires are placed outside they can affect the aesthetics of the installation, a fact which can be important in places with especial restrictions on this regard.
Another option is to set up a system which allows removing or hiding the wires while the lifting device is not being used. To do so, a pulley can be installed on the top of the tower, which allows lowering the wires when the lifting device has to be installed, and lifting them up to the pulley when the works have been finished. These operations have to be carried out from the ground, thus even in resting position, half of the length of the wires will be still visible and exposed to the environment, since they cannot be lifted beyond the pulley. Furthermore this system enforces the pulley and its support to withstand double of the load of the lifting device, due to the forces balance.